An 18-year-old man was grievously injured in a fight in Gżira late on Sunday.
The police said the argument involved the teenager, who is from Senglea, and a 26-year-old man from Msida. It took place on Triq ix-Xatt at 11.30pm.
A knife was used in the altercation.
The teenager was certified as suffering from grievous injuries at the Floriana health clinic, while the police held the 26-year-old under arrest.
Investigations are ongoing.